1. Field of the Invention
The present invention generally relates to methods, systems and apparatuses for bony fixation and more particularly to methods, systems and apparatuses adapted for fixing the bones of the spine.
2. Background of the Invention
Fixation or fusion of vertebral columns with bone or material, rods or plates is a common, long practiced surgical method for treating a variety of conditions. Many of the existing procedures involve the use of components that protrude outwardly, which may contact and damage a body part, such as the aorta, the vena cava, the sympathetic nerves, the lungs, the esophagus, the intestine and the ureter. Also, many constructions involve components that may loosen and cause undesirable problems, often necessitating further surgical intervention. Additionally, limiting the success of these procedures are the bio-mechanical features of the spine itself, whose structure must simultaneously provide support to regions of the body, protect the vertebral nervous system and permit motion in multiple planes.
As indicated above, spinal surgery for spine fusion generally involves using implants and instrumentation to provide support to the affected area of the spine while allowing the bones thereof to fuse. The technology initially evolved using bone chips around and on top of an area of the spine that had been roughened to simulate a fracture in its consistency. The area, having encountered the bone chips, would then proceed to heal like a fracture, incorporating the bone chips. However, surgical procedures dealing with the spine present notable challenges. For example, bioengineers have been required to identify the various elements of the complex motions that the spine performs, and the components of the complex forces it bears. This complexity has made it difficult to achieve adequate stability and effective healing in surgical procedures directed to the spine.
One surgical technique provided by Cloward, involves cutting a dowel type hole with a saw across or through the moveable intervertebral disc and replacing it with a bone graft that was harvested from the hip bone. This procedure limits motion and mobility and results in a fusion of the adjacent vertebral bodies. However, as a result of the complex motions of the spine, it is often difficult to secure the dowel from displacing. Further, it has become apparent over time, however, that this particular technique does not always yield a secure fusion.
Other techniques have been developed that involve the placement of various hardware elements, including rods and hooks, rods and screws and plates and screws. The dowel technique also has advanced over the past five years or so, with dowels being fabricated from cadaver bone or metals such as titanium or stainless steel. These techniques, whether using hardware, dowels or some combination thereof, have a common goal to enhance stability by diminishing movement, thereby resulting in or enhancing the potential of a fusion of adjacent vertebral bones. For example, in one of these other techniques, the disc is removed and adjacent vertebrae are positioned in a stable position by placing a plate against and traversing them, which plate is secured or anchored to each by means of screws.
In another procedure, cages in the form of two parallel circular or rectangular devices are made out of a material such as titanium or stainless steel and these devices are fenestrated. Bone is packed in the center of the devices that will heal to adjacent bone through each fenestration. In this procedure, the disc space is distracted so all ligamentous structures are taut and the bones are held in their normal maximal position of distraction. Because the cages are implanted in spongy bone, they are more likely to collapse the surrounding bone, thus resulting in loss of distraction and subsequently cage dislodgment.
U.S. Pat. No. 5,591,235 reports a certain spinal fixation device and technique for stabilizing vertebrae. In this technique, a hollow screw is inserted into a hole, preferably a hole saw recess, in each adjoining vertebrae. A channel is cut into the vertebrae, which is lined up with corresponding axial slots in the screw. A rod is inserted into the channel and so as to pass through the axial slots in the screw. The rod is secured to each of the screws by means of a locking cap. The rod also is arranged so as to provide a bridge between the hollow screws in the adjoining vertebrae. Certain disadvantages have been surmised using such a device and technique. For example, it has become apparent that the trough in the vertebral bodies destabilizes some of the cortex of the vertebrae body wall, which is the strongest component.
Thus, it would be desirable to provide a new apparatus, system and methods for spinal fixation that enhances healing of the bone while providing structural support to the spine. It would be particularly desirable to provide such an apparatus, system and method that would involve the use of open surgical or minimally invasive surgical techniques as well as a technique in which the implant burrows in the bone spine, traverses across the disk space, and ends in an adjacent or neighboring vertebrae or vertebras, providing limited or no protrusions. It also would be desirable to provide such an apparatus, system and method where the implant is retained within the bone without requiring contour-varying external vertebral wall fixation as compared to conventional devices, as such a device would avoid many of the problems associated with conventional devices such as blood vessel injury, erosion into organs, as well as placement near nerves.